Excitation system

Abstract

An excitation system (15) is disclosed for providing excitation to a main rotating electrical machine (2). The excitation system comprises an exciter (50) and an auxiliary generator (52). The exciter and the auxiliary generator have separate stator cores (14, 18) and share a common rotor core (16). The common rotor (16) core may be located between the two stator cores (14, 18). This may help to optimize space, improve material usage and reduce the total rotating mass. A mounting arrangement for the common rotor core is also disclosed.

The invention claimed is: 
     
       1. An excitation system arranged to provide excitation to a main rotating electrical machine, the excitation system comprising:
 an exciter arranged to provide excitation to the main rotating electrical machine, the exciter comprising an exciter stator core; and 
 a permanent magnet generator arranged to provide excitation to the exciter, the permanent magnet generator comprising a permanent magnet generator stator core separate from the exciter stator core; 
 wherein:
 one of the permanent magnet generator and the exciter is nested inside the other; 
 the exciter and the permanent magnet generator share a common rotor core, the common rotor core comprising a common back iron; 
 the common rotor core is substantially annular in shape; 
 exciter core windings are provided on one of a radially outwards side and a radially inwards side of the common rotor core; and 
 permanent magnets are provided on another of the radially outwards side and the radially inwards side of the common rotor core. 
 
 
     
     
       2. The excitation system according to  claim 1 , wherein the exciter core windings are provided on the radially outwards side of the common rotor core, and the permanent magnets are provided on the radially inwards side of the common rotor core. 
     
     
       3. The excitation system according to  claim 2 , wherein the common rotor core comprises slots on its radially outwards side for the exciter core windings. 
     
     
       4. The excitation system according to  claim 1 , wherein the exciter stator core is located radially outwards of the common rotor core and the permanent magnet generator stator core is located radially inwards of the common rotor core. 
     
     
       5. The excitation system according to  claim 1 , wherein the exciter stator core, the common rotor core and the permanent magnet generator stator core are laminated. 
     
     
       6. The excitation system according to  claim 5 , wherein a lamination for each of the exciter stator core, the common rotor core and the permanent magnet generator stator core is punched from a concentric part of a same sheet of raw material. 
     
     
       7. The excitation system according to  claim 5 , wherein a lamination for the permanent magnet generator stator core is stamped from an area of raw material which is inside an area from which the common rotor core is stamped, and a lamination for the common rotor core is stamped from an area of raw material which is inside an area from which the exciter stator core is stamped. 
     
     
       8. The excitation system according to  claim 1 , wherein at least one of the exciter stator core and the permanent magnet generator stator core is mounted on a bracket. 
     
     
       9. The excitation system according to  claim 8 , wherein the bracket is arranged to support a shaft of the main rotating electrical machine. 
     
     
       10. The excitation system according to  claim 8 , wherein the bracket comprises a first set of mounts which mount the exciter stator, and a second set of mounts which mount the permanent magnet generator stator. 
     
     
       11. The excitation system according to  claim 10 , wherein the bracket comprises a mating face which mates with a frame of the main rotating electric machine, a bearing support member which supports a bearing for the shaft of the main rotating electrical machine, and radial ribs extending between the mating face and the bearing support member. 
     
     
       12. The excitation system according to  claim 11 , wherein the first set of mounts which mount the exciter stator are co-located with the radial ribs, and ventilation holes are provided between adjacent ribs. 
     
     
       13. The excitation system according to  claim 1 , further comprising a rotor mount arranged to connect the common rotor core to a shaft of the main rotating electric machine. 
     
     
       14. The excitation system according to  claim 13 , wherein at least one of the rotor mount and the common rotor core comprises a protrusion which engages with a recess in the other of the rotor mount and the common rotor core. 
     
     
       15. The excitation system according to  claim 1 , wherein the common rotor core comprises slots arranged to accommodate the permanent magnets. 
     
     
       16. The excitation system according to  claim 15 , wherein a slot is formed on one side by a recess in the common rotor core and on the other side by webbing on the common rotor core. 
     
     
       17. The excitation system according to  claim 16 , wherein a plurality of slots is provided within a single webbing, and the plurality of slots within a single webbing accommodates magnets which form one pole of the permanent magnet generator. 
     
     
       18. The excitation system according to  claim 1 , wherein the permanent magnet generator comprises a stator core with a plurality of salient poles, and each of the plurality of salient poles is wound with a coil. 
     
     
       19. A rotating electrical machine comprising a main machine and an excitation system, wherein the excitation system provides excitation to the main machine, the excitation system comprising:
 an exciter arranged to provide excitation to the main machine, the exciter comprising an exciter stator core; and 
 a permanent magnet generator arranged to provide excitation to the exciter and the permanent magnet generator comprising a permanent magnet generator stator core separate from the exciter stator core; 
 wherein:
 one of the permanent magnet generator and the exciter is nested inside the other; 
 the exciter and the permanent magnet generator share a common rotor core, the common rotor core comprising a common back iron; 
 the common rotor core is substantially annular in shape; 
 exciter rotor windings are provided on one of a radially outwards side and a radially inwards side of the common rotor core; and 
 permanent magnets are provided on another of the radially outwards side and the radially inwards side of the common rotor core. 
 
 
     
     
       20. A method of manufacturing an excitation system, the excitation system comprising an exciter for providing excitation to a main rotating electrical machine, the exciter comprising an exciter stator core, and a permanent magnet generator for providing excitation to the exciter, the permanent magnet generator comprising a permanent magnet generator stator core separate from the exciter stator core, wherein one of the permanent magnet generator and the exciter is nested inside the other, the method comprising:
 manufacturing a common rotor core shared by the exciter and the permanent magnet generator, the common rotor core comprising a common back iron, wherein the common rotor core is substantially annular in shape; 
 providing exciter rotor windings on one of a radially outwards side and a radially inwards side of the common rotor core; and 
 providing permanent magnets on another of the radially outwards side and the radially inwards side of the common rotor core.